1. Technical Field
The present invention relates to the sterilization, seeding, culturing, storing, shipping, and testing of three-dimensional tissue. Specifically, the present invention relates to an apparatus and method for seeding and culturing three-dimensional tissue constructs with viable mammalian cells under simulated in vivo conditions, resulting in three-dimensional tissue that is more likely to display the biochemical, physical, and structural properties of native tissues.
2. Discussion of the Related Art
Biological implants are presently used by surgeons to repair or replace a variety of native tissues, including heart valves, arterial or venous blood vessels, articular cartilage, tendons, and ligaments, that are weakened, damaged or obstructed due to trauma or disease. Historically, implants have been either homografts, prosthetic grafts made of synthetic materials such as polyester (e.g., Dacron), expanded polytetraflouroethylene (ePTFE), and other composite materials, or fresh or fixed biological tissue grafts.
However, synthetic grafts generally have inadequate patency rates for many uses, while the harvesting of homografts requires extensive surgery which is time-consuming, costly, and traumatic to the patient. Fixed tissue grafts do not allow for infiltration and colonization by the host cells, which is essential to remodeling and tissue maintenance. Consequently, fixed tissue grafts degrade with time and will eventually malfunction.
Due to the inadequacies of these currently available synthetic and biological grafts, as well as the cost and limited supply of homografts, tissue-engineered grafts are being developed which are seeded and cultured, in vitro, with cells. For example, U.S. Pat. No. 5,266,480 to Naughton et al. discloses the establishment of a three-dimensional matrix, seeding of the matrix with desired cells, and maintenance of the culture to provide a variety of three-dimensional tissues suitable for use in different applications. Tissue-engineered grafts utilizing this technology may be superior to other grafts for use in replacement therapy in that they more closely display the long term dimensional stability and patency of native arteries and vessels with normal physiologic functionality.
Historically, the seeding and culturing of such grafts, and tissue in general, has taken place in a static environment such as a Petri or culture dish. However, there are disadvantages to seeding and culturing tissue in such an environment. For example, the lack of circulation of nutrients in these static systems results in a slow and ineffective seeding and culturing process. Moreover, a static culturing environment may lead to de-differentiation and loss of tissue function, and cannot support growth of tissue beyond a certain thickness.
In contrast, tissues that are seeded and cultured in a dynamic environment can be grown to a wider range of thicknesses, and are more likely to tolerate the physiological conditions that exist in the human body once implanted. Thus, there exists a need for an environment that is designed to simulate physiologic conditions that particular tissues would be subjected to in vivo, in which to seed and culture tissue-engineered grafts and other prosthetic devices.